Fix test suite when ext/intl isn't available

- This will hopefully enable the testsuite to run in HHVM (see: [this
  blog post](http://www.hhvm.com/blog/?p=875))
- There were a bunch of errors caused by `Zend\I18n\Validator\Int`,
  switching some tests to use `Zend\Validation\Digits` might be a good
idea